This invention relates generally to a method and apparatus for separating particles. Specifically the present invention contemplates separating the particles by density and/or by size.
A need presently exists for economically and easily removing sulfur from coal prior to combustion. Sulfur in coal is found in three common forms: Pyrite (FeS.sub.2), sulfate sulfur (e.g., gypsum, CaSO.sub.4.2H.sub.2 O), and organic sulfur. Of these, pyrite tends to be the principal source of sulfur in coal with organic sulfur and sulfate sulfur being present usually only in minor amounts. While organic sulfur content is usually low, it may in some instances be substantial. For example, in Iowa and Illinois coal the ratio of inorganic pyrite sulfur to organic sulfur is 3:2.
In addition, it is also desirable to remove certain other impurities from the coal which produce ash in the burning process. The most prominent of these include calcite (CaCO.sub.3); silica (SiO.sub.2); and certain clays including those containing sodium.
These ash impurities and the sulfur hinder the combustion process in numerous ways. They contribute significantly to the pollution in the smokestack emissions, thereby creating the need for expensive and energy consuming equipment to reduce the pollution from smokestack emissions. They also cause slag formation in the boiler, and they reduce the temperature of combustion in the boiler. By removing these from the coal, it would be possible to increase the efficiency of the burning in the boiler and also raise the temperature. Furthermore, the pollution from the smokestack would be significantly reduced, and the need for anti-pollution devices would also be reduced.